This invention relates to molecules having a first chromophore having a maximum absorption above 700 nm and an independent second chromophore having a different absorption maximum than the first chromophore.
In recent years, there is a strong need in various high technology applications for compounds that absorb in the infrared regions of the electromagnetic spectrum. Such materials can be used, for example, in laser thermal printing system, in which the donor sheet includes an IR colorant that strongly absorbs at the wavelength of the laser. When the donor is irradiated, this absorbing material converts light energy to thermal energy and transfers the heat to the colorant in the immediate vicinity, thereby heating the colorant to its vaporization temperature for transfer to the receiver. Since the local temperature can reach as high as 600xc2x0 C., infrared colorants tend to get transferred to some extent. As a result, there is some unwanted color contamination. Therefore, there is a need to have IR absorbing compounds that exhibit the same colors as the final images, so that the color contamination problem associated with laser thermal proofing can be reduced.
Secondly, there is also a need for printing inks with absorption beyond 700 nm, particularly in the near IR region. It is normally done by adding to the ink a second colorant having a separate IR chromophore, which requires co-optimization of both image ink and IR colorants. Such process is always tedious and inaccurate. Additionally, there would be an advantage to have a single compound containing both IR and image chromophore, so that there is no difference between them in term of migration rate.
In EP 499,822 A1, it is suggested to incorporate in a single molecule two independent visible colorant moieties in order to increase the visible colorant density. In U.S. Pat. No. 5,972,838, it is suggested to use a mixture of IR and visible colorants in a thermal transfer donor but this approach introduces concerns of unwanted color contamination because of unwanted incidental visible light absorption by the IR colorant and because the two colorants have different transfer rates.
It is a problem to be solved to provide an IR colorant material that exhibits good stability.
The invention provides a molecule containing a first chromophore that exhibits a first absorption maximum above 700 nm and a second chromophore that exhibits a second absorption maximum different from the first absorption maximum, wherein the absorption of the first and second chromophores are substantially independent of each other.
The molecule exhibits improved stability.